Mechanical face seals

ABSTRACT

A metal bellows for use in a mechanical seal is rolled from a flat sheet and seam welded along an axial diagonal line. The bellows includes corrugations or convolutions having inner and outer crowns of identical radii. The end corrugation or convolution at each end of the bellows is axially compressed to provide an annular double-thickness bearing and support surface against which an end ring is located in face-to-face connection. A similar bellows of multiple plies is similarly constructed using a plurality of tubular bodies.

BACKGROUND OF THE INVENTION

This invention relates to mechanical face seals and to metal bellows foruse therein.

A mechanical face seal generally comprises a rotary seal element and astationary seal element usually in the form of rings in rubbing orrunning face-to-face sealing contact, the rotary seal ring surroundingand be secured directly or indirectly to a rotary element such, forexample, as a rotary shaft and the stationary seal ring also surroundingthe rotary shaft but being secured against rotation to a stationaryelement such, for example, as a housing within-which the shaft rotates.

One of the seal elements is movable axially of the shaft and means isprovided between the housing and same to urge it into contact with theother seal element to provide the necessary sealing effect and tocompensate for wear which occurs through use in the running faces of theseal rings.

The urging means may be a mechanical spring or a metal bellows, eitherstationary or rotatable depending upon which sealing element it isassociated with, and the present invention is concerned with amechanical face seal incorporating a metal bellows as the means forapplying axial pressure and with the construction of the metal bellowsper se.

The use of metal bellows in mechanical face seals has been known formany years and in various forms such, for example, as discs (washers)welded together at alternate inner and outer diameters, or a metal tuberolled or otherwise formed into corrugated or convoluted configuration.

The mechanical face seal of this invention is concerned with a metalbellows of the latter construction.

The mechanical face seal of the present invention employs a metalbellows whereof the crowns of the corrugations or convolutions haveinner and outer radii of the same dimension.

SUMMARY OF THE INVENTION

According to the first aspect of the present invention there is provideda method of manufacturing a metal bellows comprising the steps of:

(i) rolling a flat metal strip into a tube of predetermined diameterwith a pair of opposed edges defining an open axially extending seam;

(ii) welding said opposed edges together along the seam to form a closedtube;

(iii) deforming the tube to define along the length thereofaxially-spaced corrugations or convolutions having inner and outercrowns of identical radii; and

(iv) axially compressing each end corrugation or convolution to define adouble-thickness annular end bearing and support face.

Preferably the method comprises the step of rolling the flat metal stripinto a tubular configuration whereof the pair of opposed edges define adiagonally-extending axial open seam.

Preferably the method comprises the step of welding to each annular endbearing and support face an end ring at the outer diameter of the endring and end face.

According to a second aspect of the present invention there is provideda metal bellows comprising a tubular body defining axially-spacedcorrugations or convolutions having inner and outer crowns of identicalradii, and, at each end, an annular, double-thickness, end bearing andsupport face.

Preferably the bellows is of rolled construction with an axialdiagonally-disposed welded seam.

Preferably the bellows has welded to each annular end bearing andsupport face an end ring at the outer diameter of the end face and endring.

According to a third aspect of the present invention there is provided amethod of manufacturing a metal bellows comprising the steps of:

(i) rolling a flat metal strip into a tube of predetermined diameterwith a pair of opposed edges defining an open axially extending diagonalseam;

(ii) welding said opposed edges together along the seam to form a closedtube; and

(iii) deforming the tube to define along the length thereofaxially-spaced corrugations or convolutions having inner and outercrowns of identical radii.

Preferably the method comprises the steps of welding an end of thebellows to an inner diameter of an end ring, and the other end to anouter diameter of another end ring.

According to a fourth aspect of the present invention there is providedmetal bellows comprising a rolled, diagonally-seamed tubular bodydefining axially-spaced corrugations or convolutions having inner andouter crowns of identical radii.

Preferably the bellows has one end welded to an outer diameter one endring and its other end welded to an inner diameter of another end ring.

Preferably the bellows ends lap the inner and outer circumferentialsurfaces of the respective end rings and the respective weldingconnection is made at locations axially spaced from the respectiveadjacent bellows corrugation or convolution.

As a result of the aforesaid bellows constructions the overall axiallength of a given mechanical seal is smaller than comparable existingmechanical seals since no weld bridge exists between the bellows endsand the end rings. Also the bellows is operationally stronger due toeither the weld connections to the double-thickness end bearing andsupport faces or to the fact that the weld connections are remote fromthe flexing region of the bellows.

Preferably the rolled bellows is provided with the diagonalaxially-extending weld to give increased burst pressure thereto.

Preferably the mechanical bellows is formed of a material having a goodoperational strength which can operate over a wide temperature range andwhich is corrosion resistant. A preferred but not exclusive material isthat sold under the Trade Name "INCONEL".

Preferably also the mechanical bellows is of two or more plyconstruction, preferably two ply with one thin-walled bellows fittingsnugly and intimately within the other and preferably with the diagonalwelded seams oppositely handed or inclined. As a result axial softnessis achieved without any loss of the high pressure characteristics of thebellows. This axial softness permits easier fitment of the bellowswithin the mechanical seal and copes with seal face wear withoutcompromising the sealing ability of the mechanical seal.

The two bellows plies are preferably individually sealed at each end toprovide resistance to corrosion in the event of one cracking orfracturing and also to provide a pressure sealing back-up.

The mechanical bellows of the present invention preferably, comparedwith existing bellows, has a narrow pitch and short axial length (span),preferably but not exclusively having a span to pitch ratio of between1:1 to 2:1.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a metal strip from which a bellows according tothis invention is formed;

FIGS. 2 and 3 are respectively an end view and a plan view of a seamwelded rolled tube;

FIGS. 4 and 5 are detail views showing the formation of the annular endbearing and support face;

FIG. 6 is a fragmentary longitudinal half section of a mechanical sealincorporating a bellows according to the invention;

FIG. 7 is a detail view, to an enlarged scale showing the weld betweenend ring and the bellows;

FIG. 8 is a fragmentary longitudinal half section of another embodimentof a mechanical face seal incorporating a bellows according to theinvention; and

FIGS. 9 and 10 are detail views of two further modifications of thebellows of the mechanical face seal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The tube rolling technique and the tube deformation technique to formaxially-spaced corrugations and convolutions are known to those skilledin the art of metal bellows manufacture and accordingly are notdescribed herein in detail.

The bellows according to one aspect of this invention is manufactured asfollows:

(1) a flat metal strip 10 of parallelogram configuration and, forexample, of 0.15 mm thickness is rolled to form a tube 11 of therequired length and diameter with an open, diagonally-inclined,axially-extending open seam 12;

(2) the edges 13 of the metal strip 10 defining the open seam 12 arewelded together to form a closed tube;

(3) the roll-formed and welded tube is then deformed into a bellowsconfiguration by rollers (not shown) acting on the tube wall bothinternally of the tube bore and externally; and

(4) a double-thickness annular end bearing and support face 14 is formedat each end of the bellows by axially compressing each end corrugationor convolution by a smearing action. More precisely, the terminalcorrugation or convolution 15 at each end is severed from the bellows(see arrow C) and simultaneously the adjacent corrugation or convolution16 is smeared (see arrow S) by the cutting device (not shown) into theaxially compressed configuration 16A to form the double thicknessannular end bearing and support face 14.

A preferred construction of bellows is a two ply bellows and this isachieved as follows:

(5) a pair of rolled seam-welded tubes are formed in accordance withsteps (1) and (2) described above, the length and diameters of the tubesbeing such that one can be inserted inside the other with a close fit,i.e. the outer surface of the inner tube is contiguous with the innersurface of the outer tube, with the inner tube being slightly shorter inlength than the outer tube so that it does not protrude from the latterat either end, and with the diagonal seams (see 12, 12A of FIG. 3) beingoppositely inclined or handed. and

(6) the assembly of two nesting tubes is subjected to the manufacturingsteps (3) and (4) described above.

It will be manifest that the annular end bearing and support faces of atwo ply bellows are particularly strong and robust each consisting, asit does, of four thicknesses of metal.

It will also be manifest that a bellows may be constituted by more thantwo plies of metal.

If the bellows is multi-ply then to avoid fretting between contiguoussurfaces which can cause corrosion, those surfaces are coated with aprotective layer of a suitable material containingpolytetrafluoroethylene (PTFE) which not only resists the frettingaction but also assists in lubricating these surfaces.

The rolling manufacturing process involves rolling of the metal outwardsand inwards from a mid-line to avoid excessive stretching of the metalstrip, and also to induce work hardening of the metal.

As has been mentioned previously the metal bellows 20 formed inaccordance with the present invention forms part of a mechanical sealand for this purpose end rings 21 and 22 are welded to each flatdouble-thickness annular end bearing and supporting face 23 of thebellows 20. The welding 30 is effected at the outer diameter of each endring 21, 22 and its associated and contiguous annular end face 23, eachend ring 21, 22 being formed with a weld overflow circumferential groove21A, 22A respectively.

The end ring 21 supports and carries a sealing ring or insert 24 whichmay be shrunk fitted to the end ring 21 or secured thereto in any otherconventional manner.

The sealing ring or insert 24 may, for example, be plain carbon orsilicon carbide.

In the embodiment shown in FIG. 6 the other end ring 22 is formed with anumber of angularly-spaced tapped bores 25 (only one shown) to permitthe bellows assembly 20, 21, 22 and sealing ring or insert 24 to befastened to a rotating shaft 26 of, for example a pump, or a shaftsleeve (not shown) which is, in turn, keyed to the shaft 26.

The end ring 22 is internally grooved to accommodate a sealing O-ring 27in contact with the shaft 26, or shaft sleeve if provided.

The sealing ring or insert 24 is in annular rubbing face-to-face contactwith a sealing ring or insert 28 of silicon carbide or plain carbonfixedly secured to the housing 29 of the pump, the bellows 20 providingthe necessary urging face to keep the rubbing faces in contact.

The bellows 20 is formed of "INCONEL" 625 and has, for example, a spanto pitch ratio of 2:1. It has, for example, a 6 mm span which permits itto fit into all ANSI and DIN boxes which typically has a radial space of10 mm.

The inner and outer crowns 20A, 20B of the bellows 20 have identicalradii.

The corrugations or convolutions of the bellows 20 are, as shown,parallel walled which renders the bellows 20 self cleaning as it rotatesthus rendering it suitable for aseptic usage applications.

Referring now to FIG. 8 of the drawings, this illustrates a mechanicalface seal identical to that of FIG. 6 save for the end connectionsbetween the bellows 40 and the end rings 41, 42.

It is to be noted that the bellows 40 which, like to bellows 20, is ofrolled two ply construction and diagonally seam welded does not haveannular double-thickness bearing and support faces.

The bellows 40 is welded to the end rings 41 and The bellows 40, at theend ring 41 location, has a non-convoluted end length 43 which laps theinner diameter of the end ring 41 as shown and which is welded to theend ring 41 at location 44 axially remote from the adjacent bellowsconvolution 45 the crown of which is an outer crown of the bellows 40.

At the end ring 42, the bellows 40 has a non-convoluted end length 46which laps the outer diameter of the end ring 42 as shown and which iswelded to the end ring 42 at a location 47 axially remote from theadjacent bellows convolution 48, the crown of which is an inner crown ofthe bellows 40.

The location of the weldments 44 and 47 permit, as hereinbeforementioned, the axial length of the bellows 40 and consequently themechanical face seal to be shorter than an equivalent existingmechanical seal and also obviates or mitigates any weld fracturingtendency caused by bellows flexing.

In FIG. 9, the welding connection between the bellows 40A and the endring 41A is identical with that illustrated on the left hand side ofFIG. 8, the crown of the convolution 45A, in this instance, being aninner crown of the bellows 40A.

In FIG. 10, the bellows 50 has a flat annular end face 51 which laps theinner radial face of an end ring 52 and the weld connection 53 betweenthe bellows 50 and the end ring 52 is at the outer diameter of thelatter.

It is to be understood that the bellows/end ring welded connections maybe identical, i.e. both inner diameter lapping, or both outer diameterlapping, or both radial lapping.

Alternatively any combination of the three lapping welding connectionsmay be employed in a single bellows construction.

While the corrugations or convolutions of the bellows have been shown tohave a constant pitch, they may alternatively have a varied pitch.

We claim:
 1. A method of manufacturing a metal bellows comprising thesteps of:(i) rolling a plurality of flat metal strips to form a pair ofindividual tubes of predetermined lengths and diameters, each of saidplurality of tubes having a pair of opposed edges defining a diagonalopen axially extending seam; (ii) welding the opposed edges of each ofsaid pair of tubes together along the seam to form a closed tube havinga diagonal axially-extending welded seam; (iii) inserting one tubewithin the other tube with the welded seams disposed in oppositedirections or hands to define a multi-wall tube assembly; (iv) deformingthe tube assembly to form along the length thereof axially-spacedcorrugations or convolutions having inner and outer crowns of identicalradii; and axially compressing each end corrugation or convolution todefine a multiple-thickness annular end bearing and support face.
 2. Amethod as claimed in claim 1 comprising the step of rolling each flatmetal strip into a tubular configuration whereof the pair of opposededges define a diagonally-extending axial open seam.
 3. A method asclaimed in claim 1 comprising the step of deforming the tube to definecorrugations or convolutions spaced apart by a constant pitch.
 4. Amethod as claimed in claim 1 comprising the step of deforming each tubeto define corrugations or convolutions spaced apart by a varied pitch.5. A metal bellows comprising a tubular body of rolled constructionclosed by a diagonal, axially extending welded seam and definingaxially-spaced corrugations or convolutions having inner and outercrowns of identical radii, and, at each end, an annular,double-thickness, end bearing and support face.
 6. A method ofmanufacturing a metal bellows comprising the steps of:(i) rolling a flatmetal strip into a tube of predetermined diameter with a pair of opposededges defining an open axially extending diagonal seam; (ii) weldingsaid opposed edges together along the seam to form a closed tube; and(iii) deforming the tube to define along the length thereofaxially-spaced corrugations or convolutions having inner and outercrowns of identical radii.
 7. A method as claimed in claim 6 comprisingthe step of deforming the tube to define corrugations or convolutionsspaced apart by a constant pitch.
 8. A method as claimed in claim 6comprising the step of deforming the tube to define corrugations orconvolutions spaced apart by a varied pitch.
 9. A method ofmanufacturing a metal bellows as claimed in claim 6 and for use in amechanical seal comprising the step of welding an end of the bellows toan inner diameter of an end ring.
 10. A method as claimed in claim 9comprising the step of welding the other end of the bellows to an outerdiameter of another end ring.
 11. A metal bellows comprising a rolled,diagonally-seamed tubular body defining axially-spaced corrugations orconvolutions having inner and outer crowns of identical radii and inwhich the tubular body is of multi-ply construction.
 12. A metal bellowscomprising a rolled, diagonally-seamed tubular body definingaxially-spaced corrugations or convolutions having inner and outercrowns of identical radii and in which the diagonally-extending seam isa welded seam